Low background flux telescope

ABSTRACT

A telescope design is disclosed that has at least some of its interior facing surfaces configured with corner reflectors, so that a detector operatively coupled to the telescope views itself, instead of those surfaces. The corner reflectors may be on, for example, interior facing surfaces of a conventional baffle appended to the telescope and/or minor supports or other structures inside the telescope housing that are within the detector&#39;s FOV. Likewise, the corner reflectors may be on interior facing surfaces of a baffle that is integrated into the telescope housing. In some such cases, the integrated baffle can be configured as both a baffle and a mirror support. The integrated baffle can be shaped to the F-cone between minors of a given telescope design, and/or configured to minimize or otherwise reduce the total obscuration of the baffle to improve the optical throughput.

RELATED APPLICATIONS

This application is related to U.S. application Ser. No. ______(Attorney Docket BAE20060391), filed Nov. 20, 2008, and titled“Integrated Telescope Baffle and Mirror Support” which is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to optical systems, and more particularly, totelescopes used for detecting radiation.

BACKGROUND OF THE INVENTION

Telescopes generally include optics adapted to focus radiation (e.g.,infrared, or IR radiation) onto a detector, such as a focal plane array(FPA). The FPA can be implemented with various known technology, such ascharge-coupled devices, quantum well infrared photodetectors, strainedsuperlattice, photovoltaic, photoconductive, or other such imagingdevices. The FPA can be cooled, where it is operatively coupled with aDewar cold finger or other cooling mechanism, but may also be uncooled(such as in the case of a microbolometer). Each cell of the FPAgenerates a detector current when a scene is imaged from a given fieldof view (FOV). Each detector current generated by the FPA is applied tothe input of a corresponding integrator circuit included in a FPAread-out circuit and digitized or otherwise prepared for subsequentimage processing.

In general, such radiation detectors are required to maintainperformance in the presence of radiation that is unwanted or otherwisenot of interest, including relatively intense radiation sources (solarand others) near the FOV. In such cases, a baffle can be used to preventthe undesired or so-called off-axis radiation from reaching thetelescope and detector. In conventional designs, the baffle iscantilevered off, or otherwise appended to, the entrance aperture end ofthe optical telescope. In some cases, the baffle design may incorporatesmall cell cube corner retroreflectors to reflect off-axis radiationback out the entrance aperture of the baffle.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an optical system. Theoptical system includes a telescope housing having an optical apertureand is capable of operatively coupling with a detector having a field ofview (FOV). The system also includes a mirror within the housing forreflecting radiation toward the detector, and a support for holding themirror in place on the optical axis, wherein an interior facing surfaceof the support in the FOV is configured with corner reflectors. Thecorner reflectors may be, for example, micro-machined on the surface ofthe support. Alternatively, or in addition to, the corner reflectors maybe securely attached to the surface of the support. In one specific suchembodiment, the corner reflectors are configured as corner cubes, eachhaving three mutually perpendicular faces. Some embodiments of thesystem may actually include the detector, which is for receiving on-axisradiation reflected by the minor.

The system may include a baffle operatively coupled externally to thehousing, for preventing off-axis radiation from entering the opticalaperture, wherein interior facing surfaces of the baffle in the FOV areconfigured with corner reflectors. Alternatively, or in addition to, thesystem may include an integrated baffle within the housing forpreventing passage of off-axis radiation, wherein interior facingsurfaces of the baffle in the FOV are configured with corner reflectors.The support for holding the mirror may be integrated into the baffle. Inone particular case, the integrated baffle includes a plurality ofchannels which selectively pass on-axis radiation, but eliminateoff-axis radiation (e.g., via reflection and/or absorption), and isshaped to an F-cone of the system. Alternatively, or in addition to, theintegrated baffle may include a plurality of channels each having alength and a diameter, and an aspect ratio of channel length to channeldiameter is maintained as channel length tapers down from longer outerchannels to shorter inner channels. In some embodiments, the minor is asecondary mirror, and the system further includes a primary minor forreflecting radiation that passes through the optical aperture toward thesecondary minor. In one such case, the integrated baffle is shaped to anF-cone between the primary and secondary mirrors. The secondary mirrorcan be for reflecting radiation from the primary mirror to a hole in theprimary mirror (such as in a Cassegrain configuration). The system mayinclude tertiary and quaternary mirrors, wherein the tertiary mirror isfor reflecting radiation that passes through the hole in the primaryminor toward the quaternary minor, and the quaternary mirror is forreflecting radiation from the tertiary minor to a hole in the tertiaryminor. The system can be, for example, a telescope having a Cassegrainconfiguration with a two minor re-imager (e.g., clam-shell design).

The features and advantages described herein are not all-inclusive and,in particular, many additional features and advantages will be apparentto one of ordinary skill in the art in view of the drawings,specification, and claims. Moreover, it should be noted that thelanguage used in the specification has been principally selected forreadability and instructional purposes, and not to limit the scope ofthe inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an optical system configured in accordance with an embodimentof the present invention.

FIG. 2 a is a telescope of the optical system shown in FIG. 1,configured in accordance with an embodiment of the present invention.

FIG. 2 b is a telescope of the optical system shown in FIG. 1,configured in accordance with an embodiment of the present invention.

FIG. 3 is a cross-sectional side view of an optical system configured inaccordance with an embodiment of the present invention.

FIG. 4 is a perspective view of an integrated baffle configured inaccordance with an embodiment of the present invention.

FIG. 5 is a perspective view of an optical system configured with cornerreflectors for reducing internally generated background flux, inaccordance with an embodiment of the present invention.

FIG. 6 illustrates corner reflectors formed on optical component edgeswithin the FOV of the optical system, in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A telescope design is disclosed that has at least some of its interiorfacing surfaces configured with corner reflectors, so that a detectoroperatively coupled to the telescope views itself, instead of thosesurfaces. The corner reflectors may be on, for example, interior facingsurfaces of a conventional baffle appended to the telescope and/or minorstruts or other structures inside the telescope housing that are withinthe detector's FOV. Likewise, the corner reflectors may be on interiorfacing surfaces of a baffle that is integrated into the telescopehousing. In some such cases, the integrated baffle can be configured asboth a baffle and a mirror support. The integrated baffle can be shapedto the F-cone between minors of a given telescope design, and/orconfigured to minimize or otherwise reduce the total obscuration of thebaffle to improve the optical throughput. Thus, the telescope design canbe configured to reduce both internally generated and external off-axisand stray light radiation. This design is appropriate for systems thathave optical telescopes that operate to detect, for example, IRradiation.

General Overview

There are a number of issues associated with conventional telescopedesigns. For example, when a baffle is cantilevered off the opticaltelescope, packaging and stability issues arise, particularly in thecase of a gimbaled system. In addition, appending the baffle to thetelescope substantially increases the length and weight of the opticalsystem. Other more subtle issues associated with baffles exist as well.For instance, although a baffle can be used to mitigate or reduceexternal off-axis radiation, the baffle is within the FOV of theradiation detector. Thus, the detector ‘sees’ the baffle, which canexhibit significant heat. As such, the baffle can be a source ofunwanted background flux. Other internal structures of the telescopethat are within the FOV or otherwise visible to the detector (such asminor struts or support structures) can similarly be a source ofunwanted background flux. Various optical systems (e.g., telescopes,cameras, and other embodiments of the present invention) can beconfigured to address one or more of these issues.

For instance, the structures within a telescope, such as mirror strutsor supports, can be configured with corner reflectors, so that thedetector views itself, instead of those structures. In particular, theinterior facing surfaces of the support structures visible to thedetector are micro-machined or otherwise configured with a series ofcorner reflectors that return impinging optical flux from inside theoptical system back to its source. The internal surfaces of each cornercube structure exhibit high reflectivity (therefore low emissivity) toprovide an apparent low flux background to the detector. The lower fluxbackground resulting from the support structures configured with suchcorner reflectors improves the signal-to-noise ratio (SNR) by reducingthe background noise internal to the optical system. In general, lowernoise/higher SNR increases the detection range for objects within thetelescope field of view. This technique of using corner cube reflectorson detector-facing support structures can also be used, for example,with conventional telescope designs having an external baffle, where theinterior facing surfaces (including edges) of the external baffle areconfigured with the corner cube reflectors.

In a similar fashion, telescope design having an integrated baffle asdescribed herein can also benefit from use of corner reflectors. In suchcases, interior facing surfaces (including edges) of the integratedbaffle can be configured with corner reflectors, so that the detectorviews itself, instead of the baffle. In particular, the surfaces of thebaffle visible to the detector are micro-machined or otherwiseconfigured with a series of corner reflectors that return impingingoptical flux from inside the optical system back to its source.

Further note that, unlike conventional approaches where a baffle isappended to the end of the telescope, integration of the baffle into thetelescope as described herein does not significantly increase the lengthof the telescope assembly. The integrated baffle can be used, forexample, as a minor support thereby effectively repurposing and moreefficiently using the space usually allocated within the telescopehousing for conventional minor struts. In more detail, optics making upa telescope (e.g., such as the primary and/or secondary minors of aCassegrain configuration) are typically secured in place with strutsupports that hold one or more optics in alignment with the opticalaxis. In accordance with one embodiment of the present invention, theintegrated baffle is configured as both a baffle and a minor support.

In such cases, the integrated baffle can be shaped to the F-cone, forexample, between the primary and secondary minors of a given telescopedesign to reduce the overall length of the optical system. In general,the baffle includes a plurality of channels which selectively passon-axis radiation, but eliminate off-axis radiation (e.g., viareflection and/or absorption). In some such embodiments, the aspectratio of the baffle (i.e., channel length to channel diametercross-section) is maintained as the length tapers down from the longerouter channels to the shorter inner channels. The tapering of the baffleshape from the longer outer channels to the shorter inner channelsessentially follows the envelope of the F-cone. Also, to keep the aspectratio consistent over the entire baffle, the channel diameters decreasewith decreasing channel length. In a more general sense, the baffledesign can be adjusted to minimize or otherwise reduce the totalobscuration of the baffle to improve the optical throughput.

Optical System with Integrated Baffle

FIG. 1 is an optical system configured in accordance with an embodimentof the present invention. As can be seen, the system includes atelescope 105 having an integrated baffle. The telescope 105 isoptically coupled to a detector and dewar assembly 107, which isoperatively coupled to a cold supply 109 (e.g., high-pressure nitrogengas or other suitable coolant). A read-out circuit 111 receivesdetection signals from the detector 107, and performs any processing(e.g., digitization, integration, filtering, etc) necessary forsubsequent operations (e.g., 2-D and/or 3-D image formation,discrimination between target and counter-measures, etc). A cover 103may also be provided to protect the input aperture of the telescope 105.

The optical system can be configured for any number of purposes,including surveillance, tracking/targeting, camera, or other suchsensing/imaging applications. Other supporting componentry and featuresspecific to the given application may be integrated into or otherwiseoperatively coupled to the system, as will be apparent in light of thisdisclosure. Each of the cover 103, detector and dewar assembly 107, coldsupply 109, read-out circuit 111, and any processing modules oradditional componentry (not shown) can be implemented with conventionaltechnology. The actual implementation of these conventional componentswill depend on factors such as the type of radiation being detected andthe degree of desired accuracy. As will further be appreciated,components such as the cover, dewar assembly and cold supply areoptional, and their use will depend on demands of the given application.The telescope 105 will be discussed in greater detail with reference toFIGS. 2 a through 6.

In one specific example embodiment, the detector 107 is configured witha focal plane array (FPA) to detect radiation in the IR frequency range.In one specific such case, the detector 107 is implemented as a dualmode monolithic FPA capable of switching between a passive IR mode to anactive LADAR mode, by switching the bias across the cells of the array,as described in U.S. Pat. No. 6,864,965, titled “Dual-Mode Focal PlaneArray for Missile Seekers.” In another example embodiment, the detector107 is implemented as a photodetector device capable of simultaneouslydetecting two or more selected wavelengths of light on apixel-registered basis, as described in U.S. Pat. No. 6,875,975, titled“Multi-Color, Multi-Focal Plane Optical Detector.” In another exampleembodiment, the detector 107 is implemented as a quantum dot infraredphotodetector (QDIP) FPA for sensing one or more colors, as described inU.S. Pat. No. 6,906,326, titled “Quantum Dot Infrared PhotodetectorFocal Plane Array.” In another example embodiment, the detector 107 isimplemented as a tunable quantum well infrared photodetector (QWIP) FPAthat is configured for dynamic bias-controlled spectral tunability forperforming the likes of imaging and spectroscopy, as described in U.S.Pat. No. 7,291,858, titled “QWIP with Tunable Spectral Response.” Thedetector 107 may employ enhanced optical coupling techniques to improveabsorption capability and efficiency (e.g., reflective coatings andlight-coupling gratings to prevent photons from bouncing out of detectorsensing areas, such as those described in U.S. Pat. No. 7,238,960,titled “QWIP with Enhanced Optical Coupling.” Each of the U.S. Pat. Nos.6,864,965, 6,875,975, 6,906,326, 7,291,858, and 7,238,960 is hereinincorporated by reference in its entirety.

FIG. 2 a is a telescope 105 of the optical system shown in FIG. 1,configured in accordance with an embodiment of the present invention. Ascan be seen, the telescope 105 includes a housing 201, an opticalaperture 203, a primary minor 209, a secondary minor 205, and anintegrated baffle 207. Although any number of telescope configurationscan be used, one example embodiment implements a Cassegrainconfiguration.

In particular, a Cassegrain configuration of telescope 105 includes afolded optical path achieved by primary minor 209 and the secondarymirror 205, which are both aligned symmetrically about the optical axis.The larger primary mirror 209 is a concave parabolic minor having acentral hole 209 a, and the smaller secondary minor is a convexhyperbolic minor. In operation, radiation from the FOV enters thetelescope 105 through optical aperture 203 and strikes the primarymirror 209, which reflects the radiation back to the secondary mirror205. The secondary mirror then reflects the radiation through hole 209a, toward the detector 107. Note that each mirror's particularconfiguration (e.g., convex/concave, parabolic/hyperbolic, etc) can varydepending on the particular design, and the present invention is notintended to be limited to the example mirror configurations providedherein.

The minors 205 and 209 can be implemented with conventional technology,and their respective sizes can be scaled to meet range detectionrequirements within the physical constraints of the housing 201. In theexample embodiment shown, the primary minor 209 is sized such that it isheld in place by the walls of housing 201, and the secondary mirror 205is held in place by a minor collar or partial collar formed at thecentral portion of the baffle 207 (as best shown in FIG. 4). Mirror 209may alternatively be held by one or more mirror struts extending fromthe walls of housing 201, as is sometimes done. As can be seen, thecentroid of the collar, partial collar, or other minor support means canbe substantially located on the optical axis of the system, inaccordance with some embodiments. Numerous optical configurations willbe apparent in light of this disclosure. For instance, Cassegrainvariants such as the Dall-Kirkham and Ritchey-Chretien telescopes may beemployed. In addition, the size of optical aperture 203 can also vary,for example, from 1 to 50 centimeters. In a more general sense, theoptical elements of telescope 105 can be selected based on theapplication, given performance criteria such as desired operating range,operating wavelength for respective IR and/or laser systems, andprocessing speeds. In addition, any number of techniques can be used tofacilitate imaging quality, such as techniques for eliminatingaberrations. In any such cases, one or more mirror struts or other suchmirror holding means (e.g., collars or partial collars) are integratedinto the design of the baffle 207, thereby allowing integration of thebaffle 207 into the housing 201, without significantly increasing thelength of telescope 105.

The baffle 207 operates as both a baffle and a minor support, in that itis used to mitigate off-axis radiation from reaching the detector 107and to hold the secondary mirror 205 in place on the optical axis. Thebaffle can be made from any suitable materials, such as metal (e.g.,steel, aluminum) or a reflective composite (e.g., plastic or fiberglassconfigured with an optically suitable coating). In general, the baffleincludes a plurality of channels which selectively pass on-axisradiation, but eliminate off-axis radiation (e.g., via reflection and/orabsorption). In some embodiments, the integrated baffle 207 can beshaped to the F-cone between the primary 209 and secondary 205 mirrorsof telescope 105. In some such embodiments, the aspect ratio of thebaffle (i.e., channel length to channel diameter cross-section) ismaintained as the length tapers down from the longer outer channels tothe shorter inner channels. FIGS. 3 and 4 best illustrate furtherdetails of the baffle 207, and will be discussed in turn.

The integrated baffle 207 may be configured with corner reflectors, sothat the detector 107 views itself, instead of the baffle 207. Inparticular, the surfaces of the baffle visible to the detector aremicro-machined or otherwise configured with a series of cornerreflectors that are shaped to return impinging optical flux from insidethe optical system back to its source. FIG. 6 best illustrates detailsof a baffle 207 configured with corner reflectors, and will be discussedin turn.

FIG. 2 b is a telescope of the optical system shown in FIG. 1,configured in accordance with an embodiment of the present invention.This embodiment is similar to that shown in FIG. 2 a, but furtherincludes a conventional two mirror re-imager configuration. In moredetail, the two mirror re-imager includes the addition of a convexhyperbolic quaternary mirror 211 and a concave parabolic mirror tertiaryminor 213. In operation, radiation from the FOV enters the telescope 105through optical aperture 203 and strikes the primary mirror 209, whichreflects the radiation back to the secondary minor 205. The secondarymirror then reflects the radiation through holes 209 a and 211 a, towardthe tertiary minor 213. The tertiary mirror 213 reflects the radiationback to the quaternary mirror 211, which reflects the re-imagedradiation through hole 213 a, and toward the detector 107. As previouslynoted, each mirror's particular configuration (e.g., convex/concave,parabolic/hyperbolic, etc) can vary depending on the particular design,and the present invention is not intended to be limited to the examplemirror configurations provided herein.

Each of the primary 209, secondary 205, tertiary 213, and quaternary 211mirrors can be formed individually. Alternatively, the primary 209 andquaternary 211 mirrors can be integrally formed, as is sometimesconventionally done. The mirrors 211 and 213 can be implemented withconventional technology, and their respective sizes can be scaled tomeet range detection requirements within the physical constraints of thehousing 201. In the example embodiment shown, the tertiary minor 213 issized such that it is held in place by the walls of housing 201.Alternatively, mirror 213 may be held by one or more mirror strutsextending from the walls of housing 201, as is sometimes done. Thequaternary minor 211 may also be held in place by conventional holdingmeans, or by virtue of it being integrated with the retained primarymirror 209. As previously explained, numerous optical configurationswill be apparent in light of this disclosure, and the present inventionis not intended to be limited to any particular such configurations.Rather any such configurations can be used with an integrated bafflehaving a mirror holding means, as described herein.

As previously explained with reference to FIG. 2 a, the integratedbaffle 207 may be configured with corner reflectors, so that thedetector 107 views itself, instead of the baffle 207.

FIG. 3 is a cross-sectional side view of the optical system shown inFIG. 2 a, configured in accordance with an embodiment of the presentinvention. As previously described, this example telescope 105 includesa Cassegrain configuration with a two minor re-imager, including primary209, secondary 205, tertiary 213, and quaternary 211 minors. Also notethat in this particular example, the primary 209 and quaternary 211minors are integrally formed, with the smaller quaternary mirror 211formed on the back of the larger primary mirror 209.

As can be further seen in this example embodiment, the integrated baffle207 is shaped to the F-cone 215 between the primary 209 and secondary205 minors of the telescope 105, as indicated with dashed lines. Byconforming the shape of baffle 207 to the F-cone 215 of the opticalsystem, the overall length of the optical system can be reduced. Inaddition, the mirror support (e.g., strut) that normally supports thesecondary minor 205 in conventional designs can be incorporated into thebaffle 207 further reducing the weight and optical obscuration. In suchcases, the baffle 207 performs a strut function and eliminates the needfor a separate minor support structure. The pattern (e.g., honeycomb)used to form the baffle 207 can be adjusted to minimize the totalobscuration of the baffle 207 to improve the optical throughput.

Baffle Shaped to F-Cone

FIG. 4 is a perspective view of an integrated baffle configured inaccordance with an embodiment of the present invention. As previouslyexplained, the baffle 207 can be used for off-axis rejection of lightand support for the secondary mirror 205 (or other internal opticrequiring support) in an optical telescope. The baffle 207 can be used,for example, in imaging systems that have optical telescopes thatoperate in the IR frequency range.

As can be seen in the example embodiments of FIGS. 3 and 4, the baffle207 can be contoured or tailored to the F-cone of the optical system inaddition to providing support for the secondary mirror 205. In addition,and as best shown in FIG. 4, the baffle 207 includes a minor support 401for holding the secondary minor 205 (or other optic). The support 401 inthis example embodiment is in the form of a collar, but may beimplemented as a partial collar (e.g., such as a partial collar thatcontacts the mirror perimeter at three positions approximately 120degrees apart from one another), or as conventional struts.

The openings or channels (sometimes called cells) in the baffle vary insize over the optical aperture 203. In particular, larger openings areprovided at the edge of the aperture (outer channels 403), whilerelatively smaller opening are provided near center of the aperture 203(inner channels 405) and more specifically, near the mirror support 401.This is allowed, since for a given off-axis rejection, a length todiameter (L/D or aspect ratio) is defined. The length for the bafflechannels can be longer at the edge due to the F-cone (outer channels405) and hence the diameter of those channels can be larger for aconstant L/D ratio. In general, larger diameter channels equate to loweroptical obscuration.

In some such embodiments, the aspect ratio of the baffle is maintainedas the length tapers down from the longer/wider outer channels 403 tothe shorter/narrower inner channels 405 (or otherwise follows theenvelope of the F-cone), wherein the inner channels 405 have a lengthand diameter that is about one-half of the length and diameter,respectively, of the outer channels 403. In one particular such example,the outer channels 403 are approximately 1 to 4 centimeters long and 1to 2 centimeters in diameter, and the inner channels 405 areapproximately 0.5 to 2 centimeters long and 0.5 to 1 centimeters indiameter.

The baffle 207 can be made from any suitable materials, such as metal(e.g., steel, aluminum) or reflective composite (e.g., plastic orfiberglass configured with an optically suitable coating). In addition,other baffle features can be employed that allow for use of the baffle,for example, as an RF shield or a long wave optical filter. In one suchcase, the baffle is configured to provide effective RF shielding up to afrequency defined by the cell size (e.g., honeycomb shape such ashexagons). Higher frequency radio waves would not be shielded. Inanother such case, materials that are transparent at optical radiationfrequencies, but exhibit a blocking or filtering effect to otherfrequencies can be used to encase or coat the baffle. In other suchcases, reflective baffles can be configured to reflect away externalheat loads. Other such baffle features will be apparent in light of thisdisclosure.

Corner Reflectors for Reducing Internally Generated Background Flux

FIG. 5 is a perspective view of an optical system. Each of the baffle509, telescope 501 (including mirror struts 503 and secondary minor505), and IR detector/dewar 507 can generally implemented asconventionally done. However, and in accordance with another embodimentof the present invention, the interior facing surfaces of the baffle 509and/or minor struts 503 are configured with corner reflectors 601 aswill be described in turn, and as best shown in FIG. 6. This approachcan be used for any number of systems, such as those having on-axisoptical telescopes that operate from the near to the far IR.

In a more general sense, any structure, element or support that has asurface (including any significant or non-razor thin edges) that iswithin the FOV of the detector 507 can be treated with a plurality ofcorner reflectors 601 to reduce unwanted internal IR flux. In addition,note that the baffle 509 of the example embodiment shown in FIG. 5 is aconventional baffle that is bolted or otherwise externally coupled tothe outside of the telescope 501 in front of the optical aperture. Otherembodiments may employ a telescope having an integrated baffle aspreviously described. Note that this approach is effective independentof the size or shape of the structure that is within the FOV of the IRdetector 507.

In general, the IR detector 507 of conventional telescope designsreceives flux from the mirror struts 503 which is proportional to thearea (as seen by the detector 507), emissivity and temperature. Inaddition, the IR telescope 501 is at the operational temperature of thesystem, which causes a large amount of unwanted background flux to becollected by the detector 507. To reduce this unwanted background flux,the surfaces of the struts 503 that face the detector 507 aremicro-machined or otherwise configured with corner reflectors 601 toprovide a low flux strut.

The low flux strut approach significantly reduces the optics inducedbackground flux for on-axis optical systems. This reduction allows theIR detector 507 to operate in an external background limited performanceregime. The use of a corner reflectors 601 to reduce the flux as seen byan IR detector can also be applied to the surfaces of a baffle assembly(whether external baffle 509 or internal baffle 207), or otherstructures that the detector 507 views.

FIG. 6 illustrates corner reflectors formed on optical component edgeswithin the FOV of the optical system, in accordance with an embodimentof the present invention. As can be seen, the interior facing surface603 of the baffle or support strut (or other structure) ismicro-machined with a series of corner reflectors 601 that returnimpinging optical flux from inside the optical system back to itssource. For an on-axis optical system, this becomes the cold part of thedetector/dewar assembly.

The internal surfaces of each corner cube structure are highreflectivity (therefore low emissivity) to provide an apparent low fluxbackground to the detector. For IR systems using baffles, the unwantedflux is also reduced by micromachining corner reflectors on the normalsurface of the baffle. Thus, any surfaces (including edges) in thedetector FOV can be micro-machined or otherwise configured with cornerreflectors 601. Increased SNR and detection range for objects in the FOVresults, due to reduced background flux.

The micro-machining can be carried out, for example, manually usingmetal shaping tools (e.g., files and hand lathes) on the metal surfacesof the structures within the detector FOV. Alternatively, themicro-machining can be carried out using an automatic CNC processcapable of precise and high-speed machining of the metal surfaces of thestructures within the detector FOV. To this end, conventional CNCprogramming and machining techniques can be employed to mill orotherwise form the corner reflectors 601. Alternatively, non-metallicstructures (such as plastic or composite support struts and bafflestructures) can be formed, for example, using injection moldingtechniques, wherein the mold used to form the structure includes thefeatures of the corner reflectors 601. Then, the structure integrallyformed with the corner reflector 601 features can be coated with ahighly reflective material (e.g., metal dip or spray) to form the highlyreflective corner reflectors 601. Alternatively, the corner reflectors601 can be formed as individual pieces that are then bonded or otherwisesecurely attached (e.g., glued, soldered) to the surface 603. Theseindividual pieces may be machined metal pieces (e.g., using CNCprocesses), or non-metallic pieces formed with the corner reflector 601features (e.g., injection molding) having an outer reflective layer.

In one specific embodiment, the corner reflectors 601 are configured ascorner cubes, each having three mutually perpendicular faces, as bestshown in the dashed circle of FIG. 6. In a more general sense, thereflectors 601 have the attribute of returning optical flux from insidethe optical system back in the direction it was received thereby havingthe IR detector view the cold parts (hence low flux) of the detectorassembly. The individual mirrors that form the corner reflector can be,for example, triangular (e.g., isosceles right triangles) or square orhave any other suitable shape. Theoretically, corner reflectorscomprised of square minors reflect a higher percentage of incident lightrelative to corner reflectors comprised of triangular mirrors.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

1. An optical system having an optical axis, comprising: a telescope housing having an optical aperture and capable of operatively coupling with a detector having a field of view (FOV); a mirror within the housing for reflecting radiation toward the detector; and a support for holding the minor in place on the optical axis, wherein an interior facing surface of the support in the FOV is configured with corner reflectors.
 2. The system having of claim 1 wherein the corner reflectors are micro-machined on the surface of the support.
 3. The system having of claim 1 wherein the corner reflectors are securely attached to the surface of the support.
 4. The system having of claim 1 wherein the corner reflectors are configured as corner cubes, each having three mutually perpendicular faces.
 5. The system having of claim 1, further comprising the detector, which is for receiving on-axis radiation reflected by the mirror.
 6. The system having of claim 1, further comprising: a baffle operatively coupled externally to the housing, for preventing off-axis radiation from entering the optical aperture, wherein interior facing surfaces of the baffle in the FOV are configured with corner reflectors.
 7. The system having of claim 1, further comprising: an integrated baffle within the housing for preventing passage of off-axis radiation, wherein the support for holding the mirror is integrated into the baffle and interior facing surfaces of the baffle in the FOV are configured with corner reflectors.
 8. The system of claim 7 wherein the integrated baffle includes a plurality of channels which selectively pass on-axis radiation, but eliminate off-axis radiation, and is shaped to an F-cone of the system.
 9. The system of claim 7 wherein the minor is a secondary mirror, the system further comprising: a primary minor for reflecting radiation that passes through the optical aperture toward the secondary mirror; wherein the integrated baffle is shaped to an F-cone between the primary and secondary mirrors.
 10. The system of claim 7 wherein the integrated baffle includes a plurality of channels each having a length and a diameter, and an aspect ratio of channel length to channel diameter is maintained as channel length tapers down from longer outer channels to shorter inner channels.
 11. The system of claim 1 wherein the minor is a secondary mirror, the system further comprising: a primary minor for reflecting radiation that passes through the optical aperture toward the secondary mirror; wherein the secondary mirror is for reflecting radiation from the primary minor to a hole in the primary mirror.
 12. The system of claim 11, further comprising tertiary and quaternary minors, wherein: the tertiary minor is for reflecting radiation that passes through the hole in the primary mirror toward the quaternary minor; and the quaternary minor is for reflecting radiation from the tertiary mirror to a hole in the tertiary minor.
 13. The system of claim 1 wherein the system is a telescope having a Cassegrain configuration with a two mirror re-imager.
 14. An optical system having an optical axis, comprising: a detector for receiving on-axis radiation and having a field of view (FOV); a telescope housing having an optical aperture and operatively coupled with the detector; a primary minor and a secondary mirror within the housing, the primary minor for reflecting radiation that passes through the optical aperture toward the secondary mirror, and the secondary minor for reflecting radiation toward the detector; an integrated baffle within the housing for preventing passage of off-axis radiation, and including a support for holding the secondary mirror, and interior facing surfaces of the baffle in the FOV are configured with corner reflectors.
 15. The system having of claim 14 wherein the corner reflectors are configured as corner cubes, each having three mutually perpendicular faces.
 16. The system of claim 14 wherein the integrated baffle includes a plurality of channels which selectively pass on-axis radiation, but eliminate off-axis radiation, and is shaped to an F-cone between the primary and secondary minors.
 17. The system of claim 14 wherein the integrated baffle includes a plurality of channels each having a length and a diameter, and an aspect ratio of channel length to channel diameter is maintained as channel length tapers down from longer outer channels to shorter inner channels.
 18. An optical system having an optical axis, comprising: a detector for receiving on-axis radiation and having a field of view (FOV); a telescope housing having an optical aperture and operatively coupled with the detector; a primary minor and a secondary mirror within the housing, the primary minor for reflecting radiation that passes through the optical aperture toward the secondary mirror, and the secondary minor for reflecting radiation toward the detector; and an integrated baffle within the housing for preventing passage of off-axis radiation, wherein the integrated baffle is shaped to an F-cone between the primary and secondary mirrors, and interior facing surfaces of the baffle in the FOV are configured with corner reflectors.
 19. The system having of claim 18 wherein the corner reflectors are configured as corner cubes, each having three mutually perpendicular faces.
 20. The system of claim 18 wherein the integrated baffle includes a plurality of channels each having a length and a diameter, and an aspect ratio of channel length to channel diameter is maintained as channel length tapers down from longer outer channels to shorter inner channels. 